Method of and material for coating iron and steel surfaces



Patented Apr. 6, 1954 METHOD OF AND MATERIAL FOR COATING IRON AND STEEL SURFACES William A. Callahan, Detroit, and Frank L. Gendernalik, Royal Oak, Mich., assignors to Detrex Corporation, Detroit, Mich., a corporation of Michigan N Drawing. Application June 6, 1950. Serial No. 166,544

3 Claims.

This invention relates to protective coatings for metals, and more particularly to compositions and methods for improving the appearance and the corrosion resistance of metals such as iron and steel by the deposition of a phosphate coatmg.

It has been recognized for some time that the corrosion resistance of metals such as iron and steel may be increased materially by subjecting the metal to preliminary treatment with phosphate coating compositions. Such treatment is intended to deposit a relatively tenacious phosphate coating on the surface of the metal which coating tends to prevent corrosion by resisting the action of moisture or other oxidizing or rusting influences.

Numerous additives and accelerators such as picric acid, various nitrates and the like have been suggested and some of these additives have provided improved phosphate coating results, but in many cases their accelerating effect is limited and it has been particularly difficult to produce the characteristic bluish appearance which is looked upon by the art as very desirable.

It is an object of the present invention to provide a composition and method for rapidly and economically increasing the, corrosion resistance of metals. A further object of the invention is to provide means for accelerating the action of phosphate coating compositions on metals. Still another object of the present invention is to provide compositions and methods for depositing a phosphate coating on a steel surface to produce a blue, iridescent, corrosion resistant finish there on which will serve as a base coat for the application of paints and the like.

In summary, the invention constitutes in substance a composition containing phosphate coating chemicals and licorice extract and further concerns the method for imparting a corrosion resistant coating to metal which includes the step of contacting the metal with such composition.

We have found that the action of phosphate coating compositions on metal surfaces, particularly on iron or steel surfaces, is greatly accelerated by incorporating licorice extract in the phosphate coating mix. We have further found that a bluish iridescence and improved acceleration is obtained when boric acid is incorporated into the composition in combination with licorice extract. Acceleration and formation of coatings having a bluish iridescence are both far superior when the combination of licorice extract and boric acid is used as contrasted with the results obtained where either of these materials is used alone.

The phosphate coating chemicals of the invention include broadly the chemical compounds containing the phosphate ion in an available state for coating. These chemicals include the dihydrogen ortho phosphates of such metals as sodium, potassium, iron, manganese, zinc, as well as ammonium dihydrogen ortho phosphate. Other phosphate chemicals such as the acids of phosphorus are well known to the persons skilled in the art as effective phosphate coating chemicals. Similar compounds of the meta phosphates and pyrophosphates are also effective phosphate coating chemicals and are suitable for the practice of this invention. All such compositions have an acidic etching action on iron or steel and deposit a phosphate coating thereon.

The licorice extract comprising one of the principal ingredients of the present invention is the product obtained by extracting Water soluble ingredients from licorice roots. In preparing licorice extract the licorice roots are shredded, the shredded roots and hot water are mixed to gether in a container and the mix is agitated by bubbling low pressure steam through the container. The solution is separated from the spent roots by settling and is concentrated to a thick paste in an evaporating kettle. The thick hot paste is allowed to stand at room temperature and on so cooling the paste gradually hardens to form the semi-plastic dark brown solid mass which is well known to those skilled in the licorice art and is referred to herein as licorice extract. While the proportion of licorice extract in the composition of the invention is variable within wide limits, the licorice extract must be present in proportions sufficient to act as a coating accelerator, and it is preferred to maintain the percentage by weight of licorice extract in general between -5%.

It is preferred in the practice of this invention to incorporate boric acid together with licorice extract into the phosphate coating composition. Boric acid coacts with licorice extract to provide a highly efiicient accelerator. Moreover, the use of boric acid and licorice extract gives a bluish iridescence which is highly desirable and which is not obtained if boric acid alone is used. While the proportions of boric acid in the composition are variable within wide limits, it is preferred to incorporate about 2-10% boric acid by weight into the composition of the invention.

The phosphate coating composition of the invention is conveniently made up by dissolving the phosphate coating chemicals in water, adding the desired quantity of licorice extract and boric acid to the solution, and stirring to produce a homogeneous liquid mixture. Alternatively the solid ingredients of the composition may of course be mixed together in the dry state and the phosphate coating solution may subsequently be prepared by dissolving the dry mixture in water. The amount of water incorporated in the composition preferably ranges from 5-50 times the total weight of phosphate coating chemicals, licorice extract, and boric acid.

The phosphate coating compositions of the present invention are applied to a metal surface by conventional methods, including dipping, spraying or the like. The rate of deposition of the phosphate coating film on metal is increased by subjecting the metal to a preliminary degreasing treatment prior to the coating treatment, using known degreasing chemicals such as trichlorethylene, perchlorethyelene, perchlorethane, and carbon tetrachloride.

The following examples are illustrative of preferred embodiments of the invention:

Example 1 position, rinsed, and allowed to dry. An adherent corrosion resistant coating imparting a bluish iridescence is produced on the surface of the steel sheet.

Emamplez A phosphate coating composition is prepared and heated and a piece of sheet steel is degreased, all as described in Example 1. The hot phosphate coating composition is sprayed against the sheet of steel for a period of two minutes. An adherent corrosion resistant coating, imparting to the steel a bluish iridescent appearance, is attained.

Example 3 Dihydrogen phosphate coating chemicals are prepared and a piece of iron or steel is contacted with said phosphate coating chemicals. When licorice extract in minor proportions is incorporated into said phosphate coating chemicals it is observed that the phosphate coating action on the iron or steel is accelerated, and the coating thus formed has a blue color.

While in the claims we refer to the phosphate coating chemicals as dihydrogen phosphate coating chemicals, it will be appreciated that this term is intended to include those phosphate coating chemicals which have an acidic etching action on metals such as iron and steel and contain two or more hydrogen atoms, as indicated in the foregoing specification.

While the invention has been described in detail with reference to particular embodiments thereof, it will be appreciated that modifications in procedures and substitutions of materials may be made without departing from the spirit of the invention. All such changes, including the use of certain features of the invention independently of the use of other features thereof, are within the spirit and scope of the invention as defined in the annexed claims.

Having thus described our invention, we claim:

1. A metal coating composition consisting essentially by weight of about -97 .5% dihydrogen phosphate coating chemicals, about .5-5 licorice extract, and about 2-10% boric acid.

2. A metal coating bath consisting essentially of solid ingredients in proportions by weight of about 8597.5% dihydrogen phosphate coating chemicals, about .5-5% licorice extract, and about 2-10% boric acid, said solid ingredients being dissolved in water in an amount ranging from about 5 to about 50 times the total weight of said solid ingredients.

3. A method of improving the resistance of iron or steel to corrosion comprising formulating a coating bath consisting essentially of dihydrogen phosphate coating chemicals to which have been added about 0.5-5% by Weight licorice extract and about 210% by weight boric acid dissolved in water in an amount from about 5 to about 50 times the total weight of said phosphate coating chemicals, licorice extract and boric caid, and contacting the iron or steel with the bath for a time sufiicient to form a bluish iridescent coating thereon.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,610,362 Coslett Dec. 14, 1926 2,403,426 Douty et a1 July 2, 1946 2,471,908 Snyder May 31, 1949 2,479,564 Gilbert Aug. 23, 1949 2,548,620 Chester et a1 Apr. 10, 1951 

1. A METAL COATING COMPOSITIONS CONSISTING ESSENTIALLY BY WEIGHT OF ABOUT 85-97.5% DIHYDROGEN PHOSPHATE COATING CHEMICALS, ABOUT .5-5% LICORICE EXTRACT, AND ABOUT 2-10% BORIC ACID. 